Metallicity Gradients in Cosmological Simulations Depend Strongly on Feedback Model: Forecasts for High-redshift JWST Observations

In Prep... more coming soon!

Abstract

Work in progress!

Star-Formation, Metallicity, and Stellar Mass on kpc-scales in IllustrisTNG

In Prep... more coming soon!

This work is led by Alex Qi, a former graduate student at the University of Florida. I took over this project in September 2024 and finished the analysis + wrote the paper

Abstract

Integral field unit (IFU) observations have extended our knowledge of galactic properties to kpc (or, sometimes, even smaller) patches of galaxies. These scales are where the physics driving galaxy evolution (star formation, feedback, chemical enrichment, etc) take place. Quantifying these spatially-resolved properties of galaxies, both observationally and theoretically, is therefore critical to our understanding of galaxy evolution. To this end, we investigate spatially-resolved scaling relations within galaxies at z=0 in IllustrisTNG. We examine both the resolved star-forming main sequence (rSFMS) and the resolved mass-metallicity relation (rMZR) using 1 kpc x 1 kpc maps of galaxies. We find that the rSFMS in IllustrisTNG is well-described by a power-law with an index of 0.6, but has some dependence on the host galaxy's mass. Conversely, the rMZR for IllustrisTNG can be described by a single-power-law at low surface density that flattens at high surface densities and is independent of host galaxy mass. We find quantitative agreement in both the rSFMS and rMZR with recent IFU observational campaigns. Furthermore, we argue that the nature of the rSFMS lies behind the Schmidt-Kennicutt (SK) law and local gas fraction relation, which are both independent of host galaxy properties. Finally, we construct a localized leaky-box model to study the evolution of idealized spaxels and find that this model provides a good description of these resolved relations. The degree of agreement, however, between idealized spaxels and simulated spaxels depends on the `net' outflow rate for the spaxel, and the observed scaling relations indicate a preference for a low net outflow rate.

Does the Fundamental Metallicity Relation Evolve with Redshift? II: The Evolution in Normalisation of the Mass-Metallicity Relation

Submitted to MNRAS

Abstract arXiv

The metal content of galaxies is a direct probe of the baryon cycle. A hallmark example is the relationship between a galaxy's stellar mass, star formation rate (SFR), and gas-phase metallicity: the Fundamental Metallicity Relation (FMR). While low-redshift (z lessthan 4) observational studies suggest that the FMR is redshift-invariant, recent JWST data indicate deviations from this model. In this study, we utilize the FMR to predict the evolution of the normalisation of the mass-metallicity relation (MZR) using the cosmological simulations Illustris, IllustrisTNG, EAGLE, and SIMBA. Our findings demonstrate that a z=0 calibrated FMR struggles to predict the evolution in the MZR of each simulation. To quantify the divergence of the predictions, we introduce the concepts of a ''static'' FMR, where the role of the SFR in setting the normalization of the MZR does not change with redshift, and a ''dynamic'' FMR, where the role of SFR evolves over time. We find static FMRs in Illustris and SIMBA and dynamic FMRs in IllustrisTNG and EAGLE. We suggest that the differences between these models likely points to the subtle differences in the implementation of the baryon cycle. Moreover, we echo recent JWST results at z>4 by finding significant offsets from the FMR in IllustrisTNG and EAGLE, suggesting that the observed FMR may be dynamic as well. Overall, our findings imply that the current FMR framework neglects important variations in the baryon cycle through cosmic time.

Does the Fundamental Metallicty Relation Evolve with Redshift? I: The Correlation Between Offsets from the Mass-Metallicity Relation and Star Formation Rate

Accepted to MNRAS 05/13/2024!

Check out: talk about this project.

Abstract arXiv MNRAS Github Repo

The scatter about the mass metallicity relation (MZR) has a correlation with the star formation rate (SFR) of galaxies. The lack of evidence of evolution in correlated scatter at z>2.5 leads many to refer to the relationship between mass, metallicity, and SFR as the Fundamental Metallicity Relation (FMR). Yet, recent high-redshift (z>3) JWST observations have challenged the fundamental (i.e., redshift-invariant) nature of the FMR. In this work, we show that the cosmological simulations Illustris, IllustrisTNG, and EAGLE all predict MZRs that exhibit scatter with a secondary dependence on SFR up to z=8. We introduce the concept of a "strong" FMR, where the strength of correlated scatter does not evolve with time, and a "weak" FMR, where there is some time evolution. We find that each simulation analysed has a weak FMR -- there is non-negligible evolution in the strength of the correlation with SFR. Furthermore, we show that the scatter is reduced an additional ~10-40% at z>3 when using a weak FMR, compared to assuming a strong FMR. These results highlight the importance of avoiding coarse redshift binning when assessing the FMR.

Interplay of Stellar and Gas-Phase Metallicities: Unveiling Insights for Stellar Feedback Modeling with Illustris, IllustrisTNG, and EAGLE

Accepted to MNRAS 03/12/2024!

Abstract arXiv MNRAS Github Repo

The metal content of galaxies provides a window into their formation in the full context of the cosmic baryon cycle. In this study, we examine the relationship between stellar mass and stellar metallicity (MZ*R) in the hydrodynamic simulations Illustris, TNG, and EAGLE to understand the global properties of stellar metallicities within the feedback paradigm employed by these simulations. Interestingly, we observe significant variations in the overall normalization and redshift evolution of the MZ*R across the three simulations. However, all simulations consistently demonstrate a tertiary dependence on the specific star formation rate (sSFR) of galaxies. This finding parallels the relationship seen in both simulations and observations between stellar mass, gas-phase metallicity, and some proxy of galaxy gas content (e.g., SFR, gas fraction, atomic gas mass). Since we find this correlation exists in all three simulations, each employing a sub-grid treatment of the dense, star-forming interstellar medium (ISM) to simulate smooth stellar feedback, we interpret this result as a fairly general feature of simulations of this kind. Furthermore, with a toy analytic model, we propose that the tertiary correlation in the stellar component is sensitive to the extent of the ``burstiness'' of feedback within galaxies.

Gas-phase metallicity break radii of star-forming galaxies in IllustrisTNG

Accepted to MNRAS 12/16/2022!

Check out: Slides and talk about this project.

Abstract arXiv MNRAS Github Repo

We present radial gas-phase metallicity profiles, gradients, and break radii at redshift z = 0 - 3 from the TNG50-1 star-forming galaxy population. These metallicity profiles are characterized by an emphasis on identifying the steep inner gradient and flat outer gradient. From this, the break radius is defined as the region where the transition occurs. We observe the break radius having a positive trend with mass that weakens with redshift. When normalized by the stellar half-mass radius, the break radius has a weak relation with both mass and redshift. To test if our results are dependent on the resolution or adopted physics of TNG50-1, the same analysis is performed in TNG50-2 and Illustris-1. We find general agreement between each of the simulations in their qualitative trends; however, the adopted physics between TNG and Illustris differ and therefore the breaks, normalized by size, deviate by a factor of ~2. In order to understand where the break comes from, we define two relevant time-scales: an enrichment time-scale and a radial gas mixing time-scale. We find that the break radius occurs where the gas mixing time-scale is ~10 times as long as the enrichment time-scale in all three simulation runs, with some weak mass and redshift dependence.